1. Field of the Invention
The present invention is related to the field of ocular health, disease and degeneration and, more particularly, to a noninvasive system and objective method for analyzing macular function and thereby detecting macular changes and degradations, which may be predictive of future age-related macular degeneration.
2. Description of the Related Art
Human longevity is extending, and we are increasingly subject to adverse physiological changes which are detrimental to our well-being and independence. Loss of visual acuity, which may or may not lead ultimately to blindness, can be debilitating. The macula lutea, a small area lying slightly lateral to the center of the retina, represents the region of maximum visual acuity in the human eye. While many age-related ocular changes such as cataract formation, adult-onset diabetes, and glaucoma can be reasonably well-managed so that visual self-sufficiency can be maintained, Age-related Macular Degeneration (AMD) impacting the macula lutea is progressively the most debilitating exception.
Evaluation of the macula lutea has traditionally been limited to subjective testing. By definition, subjective testing is flawed and individually anecdotal, due to total reliance on patient responses.
The earliest subjective test for patient awareness of macular changes is a graphed target known as the Amsler Grid, which requires visualization, mental evaluation, verbalized response, and remembrance for comparison with the same test conducted at an earlier time. This is inherently unreliable. There are many other subjective tests, including contrast sensitivity testing, kinetic and static perimetry, subjective manifest refraction, and color discrimination testing, but these are also anecdotal because of reliance on articulated responses, and therefore incorporate whatever subjective bias may be present. In addition, the subjectivity of any type of testing is compounded by the subjective interpreted experience/bias of the test proctor.
By the time an ophthalmoscopic examination reveals observable changes in the macula, the disease process is well established. Similarly, by the time the patient notices significant loss of visual acuity, that is uncorrectible, and/or distortion of the Amsler Grid, the disease process is well established. Current therapies include Photo-Dynamic Therapy and Macular Translocation which are medical interventions principally used when the AMD disease process has been well established and there are serious decrements in visual acuity.
It is estimated that AMD affects 20% of the population over age 65 and 37% of the population over age 75. The inference must be that the tendency toward AMD exists at an undiagnosed pre-clinical level at much earlier ages.
There is, therefore, a need for objective assessment of macular function, starting early in life, to identify any pre-disposition to develop AMD. This would then stimulate the search for constructive prophylactic strategies to forestall the future onset/progression of the disease.
In view of the foregoing, one object of the present invention is to provide an objective system and method for assessing macular function.
Another object of the invention is a system and method for objectively assessing macular function on an ongoing basis, beginning early in life, so as to detect any type of macular and other possible ocular changes, including AMD in preliminary stages, and determine risk factors associated with AMD for AMD prediction.
A further object of the invention is a system and method using selective light-wave stimulation to induce physiologic responses that indicate that macular or other possible ocular changes are occurring.
A still further object of the invention is a system and method for objectively determining AMD using visible blue light to induce a fixation reflex and/or optokinetic nystagmus.
In accordance with this and other objects, the present invention is directed to a system and method for objectively and non-invasively testing for macular and/or other ocular changes. According to the method, a narrow band of blue light within the visible light spectrum is alternately beamed at a patient""s eye through two distinct apertures in a mask which are separated by a relatively small angle of subtendance at the entrance pupil. In the event of a healthy macula, the blue light is filtered out and the patient will not exhibit a fixation reflex. If the macula is in the process of degenerating, however, the impinging of the narrow band of blue light upon the macula, via the alternate apertures, should evoke the fixation reflex. Because the fixation reflex is involuntary, the method of the present invention allows macular health to be objectively determined.
The system includes a plurality of targets separated from one another by a distance, each target emanating a specified wavelength of visible blue light. The plurality of targets are illuminated sequentially or alternately such that only one target is fully illuminated at any given point in time. An examiner observes the eye of the patient using a magnification system with a stenopaic slit for narrowing a lateral field of view of a vertical-line image to be perceived by the examiner. As the targets are sequentially illuminated, an involuntary reaction will be induced to some degree in the patient""s eye, if such individual has undergone some macular changes (which may later lead to macular degeneration.
These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.